Characterization of inhibitor of differentiation (Id3) gene expression in the developing cochlear tissue of rats.

Conclusion: The Id3 gene is expressed in the developing cochlear tissue and participates in the development of cochlear progenitor hair cells during the embryonic stage.

Objectives: Inhibitor of differentiation (Id3) is an important transcription factor expressed in the cochlear tissue and progenitor hair cells. It is likely to be involved in cell-cycle progression and the proliferation of cochlear progenitor hair cells during the embryonic stage. The dynamic expression of Id3 in the developing cochlear tissue is, however, poorly understood. In this study we sought to characterize the expression of Id3 in the developing cochlear tissue and to explore its role in the growth and proliferation of progenitor hair cells.

Material And Methods: Expression of the Id3 gene in the developing cochlear tissue was examined by means of Northern blotting, in situ hybridization and immunohistochemistry. The effects of Id3 on primary cultures of otocyst epithelial cells and a progenitor hair cell line (OT12) were studied using specific antisense oligonucleotides.

Results: The Id3 gene was expressed in the rapidly growing otocyst on embryonic Day 12 and specifically in the fundamental structures of the cochlea, e.g. the organ of Corti, spiral ganglions and stria vascularis, on postnatal Day 1. Inhibition of Id3 gene expression with antisense oligonucleotides in cultured otocyst epithelial cells and OT12 reduced DNA synthesis and cell-cycle progression, suggesting that Id3 participates in the proliferation of cochlear progenitor hair cells.